The present invention relates to tools useful for producing compression molded articles.
Traditionally, one method for producing molded articles has been to place a molding material between spaced apart, relatively movable tool halves, each tool half comprising a press platen supporting a die or mold on a molding press for shaping the desired article. The mold press or tool is then closed, resulting in the application of pressure to the molding material, which flows to fill the mold cavity created by the closing tool. Depending on the particular material used to create the molded article, the tool may be heated or cooled during the molding process. Subsequently, the tool is opened and the newly molded article is removed from the tool. This traditional molding operation is capable of producing a large number of articles at a rapid rate.
A major disadvantage of the traditional compression molding process is that significant post-molding processing is required in some instances to produce a commercially acceptable article, which puts compression molding at a competitive disadvantage with injection molding processes. The need for these post-processing operations stems from at least two sources, one of which is "flashing" -- excess material that is created at the edge of molded parts during the compression molding process. Flashing arises from the inherent nature of the traditional compression molding process. That is, in this process the molding material begins to flow when pressure is applied to it. At that moment, however, the mold cavity is not yet formed and will not be completely formed until the tool completely closes. In other words, until the moment of tool closing, the molding material is flowing within an incompletely formed mold cavity. To retain the material in the cavity as the tool closes, the tool has sliding shear edges on the tool perimeter that can draw molding material into the gap between the opposed sliding edges, thus producing the flashing. If the molding material is fiber reinforced, the flashing at the edge of the article may include protruding reinforcing fibers, which are especially unacceptable in a consumer market. Flashing must be removed after molding by a separate process and at an additional cost to the manufacturer.
A second disadvantage of the traditional compression molding process is that apertures of a desired configuration may be placed in the molded article during the molding process only in the line of draw; that is, they must have an axis that lies parallel to the direction of tool closing. The apertures are created by the extension of a core pin from one of the tool halves into an appropriately configured receiving hole in the other tool half. Apertures cannot be formed non-parallel to the line of draw since to make such apertures the non-parallel core pins can be set in place only at the moment of closing of the tool halves. That is because until that moment the pin and the receiving hole will not be in alignment with each other. The core pins, however, need to be set in place before that instant in time or the pin receiving holes will fill with the already flowing molding material. Therefore, to add apertures to the article that are non-parallel to the line of draw, the manufacturer must undertake post-processing operations to insert apertures where desired.
It would be desirable to have a compression molding tool capable of substantially eliminating flashing and that produces apertures at any desired angle in the molded article, thereby reducing post molding processing operations and expenses.